The choice to exercise or not sometimes depends on the sickness or disease. Our bodies work harder and use more energy when we are fighting an illness. If symptoms are above the neck (sore throat, runny nose), it is probably okay to exercise. If you're sick but still want to exercise, simply reduce your intensity and duration. You should not exercise if you have body aches, fever, diarrhea or vomiting, shortness of breath or chest congestion, dizziness or light-headedness. When resuming your regular exercise routine, try starting with 50% effort and 50% duration.
Loyola University Health System, November 2012